Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 04 May 2015, 15:22

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# P1 and P2 are both prime

Author Message
TAGS:
Intern
Joined: 22 May 2006
Posts: 1
Followers: 0

Kudos [?]: 0 [0], given: 0

P1 and P2 are both prime [#permalink]  11 Oct 2007, 07:33
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
Can any on pls explain why the answer is C. Thanks.

P1 and P2 are both prime. Determine p1

1. p2 - p1 = 2
2. (p2)^2 - (P1)^2 = 120
SVP
Joined: 01 May 2006
Posts: 1805
Followers: 8

Kudos [?]: 99 [0], given: 0

Welcome to GMAT Club !

Yes... (C) it is

Stat1
p2-p1 = 2

o If p2 = 7 then p1 = 5
o If p2 = 5 then p1 = 3

INSUFF.

Stat2
(p2)^2 - (P1)^2 = 120

That implies,
o (p2 - p1)*(p2 + p1) = 6 * 20 => p2 = 13 and p1 = 7
or
o (p2 - p1)*(p2 + p1) = 4 * 30 => p2 = 17 and p1 = 13
or
o (p2 - p1)*(p2 + p1) = 2 * 60 => p2 = 31 and p1 = 29

INSUFF

Both 1 and 2
2*(p2+p1) = 120
<=> p2+p1 = 60
<=> p2=31 and p1=29

SUFF.
Intern
Joined: 09 Oct 2007
Posts: 17
Followers: 0

Kudos [?]: 0 [0], given: 0

Re: DS : Prime [#permalink]  11 Oct 2007, 08:05
skyjuice wrote:
Can any on pls explain why the answer is C. Thanks.

P1 and P2 are both prime. Determine p1

1. p2 - p1 = 2
2. (p2)^2 - (P1)^2 = 120

1.There are many primes with difference 2, e.g. 3 and 5, 5 and 7. Therefore, 1 in INSUFF.

2. There are only two primes that satisfy this equation and differ by 2.

In fact, I was not sure whether there were more than two primes that satisfied just (2). 120 is not much, and if we try to put some numbers, we will see that difference between p1^2 and p2^2 becomes larger and larger after 29 and 31. However, then I tried 11 and 1. It is C.
Intern
Joined: 09 Oct 2007
Posts: 17
Followers: 0

Kudos [?]: 0 [0], given: 0

Re: DS : Prime [#permalink]  11 Oct 2007, 08:38
JingChan wrote:
Note: 1 is not a prime number ;P

Eeerr... Yes, that is right. It is an exception (found that in an old notebook). Then who can find another 2 primes that satisfy the second equation?
Manager
Joined: 13 Jul 2007
Posts: 123
Followers: 2

Kudos [?]: 4 [0], given: 0

Fig

Do I have to try and eliminate all possibilities (or consider those multiple poss) when I solve st 2 bcos I wudnt even remember and knock st2 when I see

(p2 + p1)(p2-p1) = 120
SVP
Joined: 01 May 2006
Posts: 1805
Followers: 8

Kudos [?]: 99 [0], given: 0

lnaik wrote:
Fig

Do I have to try and eliminate all possibilities (or consider those multiple poss) when I solve st 2 bcos I wudnt even remember and knock st2 when I see

(p2 + p1)(p2-p1) = 120

To me, we just need to be sure that the statment 2 is valid or not.... So finding 2 cases that bring 2 different answers is what we need here
Director
Joined: 11 Jun 2007
Posts: 932
Followers: 1

Kudos [?]: 70 [0], given: 0

OlgaN wrote:
Fig wrote:
Welcome to GMAT Club !

Yes... (C) it is

Stat1
p2-p1 = 2

o If p2 = 7 then p1 = 5
o If p2 = 5 then p1 = 3

INSUFF.

Stat2
(p2)^2 - (P1)^2 = 120

That implies,
o (p2 - p1)*(p2 + p1) = 6 * 20 => p2 = 13 and p1 = 7
or
o (p2 - p1)*(p2 + p1) = 4 * 30 => p2 = 17 and p1 = 13
or
o (p2 - p1)*(p2 + p1) = 2 * 60 => p2 = 31 and p1 = 29

INSUFF

Both 1 and 2
2*(p2+p1) = 120
<=> p2+p1 = 60
<=> p2=31 and p1=29

SUFF.

Can be p1 and p2 for example 37 and 23, 17 and 47 etc? Why exactly 31 and 29?
Thanks.

it has to satisfy either both statements:
1)p2-p1 = 2
31-29 = 2
all the other primes you listed does not

2) (p2)^2 - (P1)^2 = 120
(p2 - p1)*(p2 + p1) = 120
same as above.. again your examples does not hold true for this stmt
Similar topics Replies Last post
Similar
Topics:
If p1 and p2 are the populations and r1 and r2 are the 0 31 Jul 2014, 07:43
16 If p1 and p2 are the populations and r1 and r2 are the 12 18 Sep 2012, 02:26
if p1 and p2 are the populations and r1 & r2 are the 3 11 Jul 2009, 09:28
If P# =P/P-1 what is P##? P/(P-1) 1/P P 2 - P P 3 23 Jun 2007, 13:29
P = p1 p2 p3 is a product of three distinct primes. 4 22 Oct 2006, 19:37
Display posts from previous: Sort by